LONDON (AP) Three-time defending champion Hungary against gold medal-favorite Serbia. On the first day, too.

This is quite the match for the opening slate of the men's water polo tournament at the London Games.

The Hungarians haven't lost at the Olympics since 2000, running up a 17-match unbeaten streak along the way, and are seeking an unprecedented fourth consecutive title. Serbia, meanwhile, has been the most consistent team in the past few years, winning a slew of titles, including the 2012 European crown.

With Serbia first up, the Hungarians know they are facing a difficult challenge from Day 1 while trying to defend their title against a deep field of medal contenders.

"Serbia's one of the favorite teams to win this tournament, so it is a very tough match to start the games," said Hungary star Tamas Kasas, who is appearing in his fifth Olympics.

"We know that we are the three-time defending champions, and this gives us confidence and maybe (puts) more pressure on the other teams because they maybe won world championships and European championships, but now they have to win the most important thing."

With a record nine water polo golds, Hungary has clearly demonstrated its ability to win Olympic titles.

Serbia, meanwhile, is still in search of its first as an independent nation.

Led by two of the sport's biggest stars in Vanja Udovicic and Filip Filipovic, the Serbs took home the silver medal at the 2011 worlds, then won the European Championship this year.

"For the past four years we have made some impressive results that are putting the Serbian team as one of the favorites for the gold," Filipovic said. "In the end, the competition will show whether we are ready to handle all the pressure."

While much of the attention in the run-up to the games has focused on the Serbs, Filipovic was quick to remind people not to overlook Hungary.

"They are really scary if you are watching videos, and we've been watching videos of them for two months - how they shoot, how they defend, they are very aggressive," he said. "It's difficult to stop them."

Hungary-Serbia is the marquee matchup on the first day, but there are a handful of other top-class games on the docket.

The 12-team field is broken down into two groups of six for the preliminary stage, and the top four teams from each group advance to the knockout round.

Hungary and Serbia are joined in a tough Group B by the United States, Montenegro - both serious medal contenders - as well as Romania and Britain.

The U.S., which is looking to improve on its silver medal-finish four years ago in Beijing, starts its campaign in London against a talented Montenegro side that finished second at the 2012 European Championship, losing to Serbia 9-8 in the final.

"I think it's a great team to open with," said U.S. captain Tony Azevedo, who is one of 10 veterans from the Americans' 2008 squad.

"You want to start off strong, and team Montenegro is one of the strongest teams out there. We have more guys who have been to Olympics than they have, so hopefully the jitters will be more on their side than ours."

In Group A, perennial power Croatia opens against a resurgent Greece team that has legitimate medal hopes. Spain faces Kazakhstan and 2011 world champion Italy meets Australia.